1. Field of the Invention
The present invention relates generally to the field of equalizers for equalizing the output pressures of at least two valves, and more particularly to an improved equalizer which is particularly adapted for use in a redundant force-summed control system.
2. Description of the Prior Art
In earlier years, flight control surfaces, such as rudders, elevators and ailerons, were mechanically connected to the pilot's hand controls. Such mechanical systems have been largely replaced by electrohydraulic servosystems, in which the pilot's commands are transmitted electrically to servoactuators. While such "fly-by-wire" servosystems offer the advantage of increased performance, it has been appreciated that a failure of one component can have a dramatic adverse effect on system performance. Concerns for safety have led to the development of redundant (i.e., multiple channel) servosystems, such that effective control may be continued notwithstanding a failure in one system component. As described in Technical Bulletin 127, entitled "Redundant Electrohydraulic Servoactuators", Moog Inc. (1976), such servoactuators have heretofore been provided with "simple parallel", "averaging", "majority voting", "mid-value", "detection-correction", and "hydrid" types of redundancy. All of these approaches seek to permit continued control, albeit sometimes at the expense of some aspect of performance, in the event of a failure in a system component.
Some of these earlier approaches are also disclosed in U.S Pat. Nos. 3,257,911, 3,270,623 and 3,741,073.